Aboard an oceanographic cable laying ship a cable fleeting drum is provided to facilitate an oceanographic cable laying/recovery operation.
The fleeting drum includes a pair of spaced fleeting flanges mounted at opposite sides thereof and a plurality of endless conveyors arranged for side-to-side movement between the flanges parallel to the axis of the drum. Outward surfaces of the endless conveyors form the peripheral surface of the drum. The conveyors are simultaneously driven in a given direction by a driving mechanism which is operative as the drum is rotated about its axis and thereby "fleets" or moves a cable wound over the drum from one side of the drum to the other.
In preparation for a cable laying operation, a leading end of a cable is wound about the periphery of the drum from an entry side of the drum adjacent to one fleeting flange to an exit side of the drum adjacent to the other fleeting flange. The fleeting drum is then driven about its axis thereby drawing successive portions of the cable onto the entry side of the drum as the conveyors are simultaneously driven in the given direction towards the exit side of the drum. In this manner, successive portions of the cable are drawn onto the peripheral conveyor surface of the drum and are moved or "fleeted" from the entry side of the drum to the exit side of the drum for subsequent lowering to the ocean floor from the exit side. In this process, the conveyors are intended to facilitate smooth uninterrupted payout or pickup of the cable during the cable laying/recovery operation.
The fleeting flanges are provided to retain the cable on the peripheral surface of the drum and are mounted at close tolerances above the surface of the conveyors so as to prevent cable having smaller diameters from becoming trapped or pinched between the conveyors and the fleeting flanges during the cable laying operation.
In the past, the conveyors included a plurality of interconnected load links each having two spaced bearing shafts with a set of roller bearings axially mounted on each shaft. An upper run of the conveyor was supported in a frame of the module having continuous planar support surfaces. The roller bearings of the load links slidably engaged the continuous planar support surfaces of the frame. Consequently, the load links on the upper run of the conveyor were positioned in one plane as the conveyor moved from one side of the drum to the other.
However, under certain loading conditions of the cable fleeting drum, wherein the load was not positioned directly over or between the two sets of roller bearings, one or more of the load links would pivot about one of the bearing shafts. As a result, one edge of the pivoting load links would protrude above the normally planar surface of the conveyor. The protruding edge of the load links would strike lower portions of the fleeting flanges, thus stopping the forward movement of the conveyor and causing severe damage to the driving mechanism thereof.
Furthermore, if a fleeting module was rendered inoperable because of bearing failure, the cable laying operation had to be discontinued until the inoperable fleeting module could be completely removed from the fleeting drum and replaced with a spare module. Because of the construction of the modules, the bearings on the conveyors could not be replaced without first removing the module from the drum. In addition, the effects of rust and corrosion on various portions of the conveyors usually prevented the removal of the conveyor from the module or the removal of the bearings from the conveyor without the aid of special tooling and equipment normally not available aboard ship. Therefore, the inoperable modules had to be returned to port for replacement of the bearings.
Unless there were spare modules aboard ship, the cable laying operation would have to be totally abandoned so that the ship could return to port to repair or replace the inoperable cable fleeting modules. This resulted in a time consuming and costly effort which usually required that the ship be placed out of service for an extended period of time.
Another past apparatus which includes a drum with several endless conveyors arranged to form the peripheral surface of the drum is disclosed in U.S. Pat. No. 3,081,658 to F. Witschi. The apparatus is provided to facilitate the cutting of a continuous strip of fabric from a wide web of fabric material. Successive portions of the fabric web are wound over the drum and are continuously moved from one side of the drum to the other by the endless conveyors as the drum rotates about its axis. The successive portions of the web are moved into engagement with a cutting wheel which continuously cuts narrow strips of fabric from the wide web.
Further, U.S. Pat. No. 3,840,112 to Walter J. Harting discloses a traveling endless grate conveyor having means for guiding the traveling conveyor along a predetermined path of travel. An upper run and a lower run of the conveyor are supported by guide roller bearings and include detachable adjustable thrust buttons which cooperate with stationary thrust plates positioned along the path of travel of the conveyor to limit drift or misalignment of the moving conveyor.